This invention relates in general to vehicle driveshafts, and in particular to a vehicle driveshaft tube having a noise reduction structure contained therein.
Torque transmitting shafts are widely used for transferring rotational power between a source of rotational power and a rotatably driven mechanism. An example of a torque transmitting shaft is a driveshaft tube used in a vehicle driveshaft assembly. The driveshaft assembly transmits rotational power from a source, such as an engine, to a driven component, such as a pair of wheels. A typical vehicle driveshaft assembly includes a hollow cylindrical driveshaft tube having an end fitting secured to each end thereof. Usually, the end fittings are embodied as end yokes which are adapted to cooperate with respective universal joints. For example, a driveshaft assembly of this general type is often used to provide a rotatable driving connection between the output shaft of a vehicle transmission and an input shaft of an axle assembly for rotatably driving the vehicle wheels. Traditionally, driveshaft tubes were made from steel. More recently, aluminum driveshafts have been developed because of their lighter weight.
One problem encountered by all types of driveshaft assemblies is their tendency to produce and transmit sound while transferring the power of the engine to the axle assembly. It is known that any mechanical body has a natural resonant frequency. This natural resonant frequency is an inherent characteristic of the mechanical body and is based upon many factors, including its composition, size and shape. The natural resonant frequency is made up of many sub-frequencies, often referred to as harmonics. As the vehicle is operated through its normal speed range (i.e. from 0 mph to about 80 mph), the rotational velocity of the driveshaft assembly changes (i.e. from 0 rpm to about 5000 rpm). As the rotational velocity of the driveshaft changes, it passes through the harmonic frequencies of the body's resonant frequency. When the rotational velocity of the driveshaft passes through these harmonic frequencies, vibration and noise may be amplified since the two frequencies are synchronized and the rotational energy of the driveshaft is converted into vibration and noise. This noise can be undesirable to passengers riding in the vehicle. Thus, it would be advantageous to deaden or reduce the sound produced by a vehicle driveshaft assembly in order to provide the passengers with a more quiet and comfortable ride.
Various attempts have been made to deaden the sound produced by vehicle driveshaft tubes. One general direction that many of these attempts have followed is to place a noise absorbing/deadening structure within the driveshaft. For example, one attempt involves disposing a hollow cylindrical cardboard insert inside an aluminum driveshaft tube to deaden the sound. However, the cardboard insert required external rubber ribs to prevent it from sliding inside the aluminum driveshaft tube. As a result, the cardboard insert is relatively complicated and expensive to employ. Other attempts at deadening the sound involve completely or partially filling the driveshaft tube with relatively non-resonant material such as steel wool, cotton, and even plaster. The use of plugs of compressible and slightly resilient material such as cork or rubber has also been suggested.
As exemplified by the number of proposed solutions to the sound problem in driveshafts, the particular solution for a specific type of driveshaft is not always straightforward. For instance, there are questions concerning what types of materials are most effective and suitable for the type of driveshaft employed. In addition, there are questions concerning the added weight, cost and performance of the material chosen for the noise reduction structure. Thus, it would be desirable to provide a noise reduction structure for an aluminum-based driveshaft tube which is lightweight, inexpensive, and long-lasting. In addition, it would particularly be desirable to provide this lighter, less expensive noise reduction structure for an aluminum-based driveshaft tube which is as or more effective in reducing the sound levels of such a driveshaft tube than the known noise reduction structures and mechanisms.